1. Field of the Invention
The present invention pertains to photoimaging and, in particular, the use of photoresists (positive-working and/or negative-working) for imaging in the production of semiconductor devices. The present invention also pertains to novel fluorine-containing polymer compositions which are useful as base resins in resists and potentially in many other applications.
2. Description of Related Art
Polymer products are used as components of imaging and photosensitive systems and particularly in photoimaging systems such as those described in Introduction to Microlithography, Second Edition by L. F. Thompson, C. G. Willson, and M. J. Bowden, American Chemical Society, Washington, D.C., 1994. In such systems, ultraviolet (UV) light or other electromagnetic radiation impinges on a material containing a photoactive component to induce a physical or chemical change in that material. A useful or latent image is thereby produced which can be processed into a useful image for semiconductor device fabrication.
Although the polymer product itself may be photoactive, generally a photosensitive composition contains one or more photoactive components in addition to the polymer product. Upon exposure to electromagnetic radiation (e.g., UV light), the photoactive component acts to change the rheological state, solubility, surface characteristics, refractive index, color, electromagnetic characteristics or other such physical or chemical characteristics of the photosensitive composition as described in the Thompson et al. publication supra.
For imaging very fine features at the submicron level in semiconductor devices, electromagnetic radiation in the far or extreme ultraviolet (UV) is needed. Positive working resists generally are utilized for semiconductor manufacture. Lithography in the UV at 365 nm (I-line) using novolak polymers and diazonaphthoquinones as dissolution inhibitors is a currently established chip technology having a resolution limit of about 0.35-0.30 micron. Lithography in the far UV at 248 nm using p-hydroxystyrene polymers is known and has a resolution limit of 0.35-0.18 nm. There is strong impetus for future photolithography at even shorter wavelengths, due to a decreasing lower resolution limit with decreasing wavelength (i.e., a resolution limit of 0.18-0.12 micron for 193 nm imaging). Photolithography using 193 nm exposure wavelength (obtained from an argon fluorine (ArF) excimer laser) is a leading candidate for future microelectronics fabrication using 0.18 and 0.13 μm design rules. Photolithography using 157 nm exposure wavelength (obtained using an F2 laser source) may be used for future microelectronics fabrication using 0.100 μm or less design rules. The opacity of traditional near UV and far UV organic photoresists at 193 nm and shorter wavelengths precludes their use in single-layer schemes at these wavelengths.
Some resist compositions suitable for imaging at 193 nm are known. For example, photoresist compositions comprising cycloolefinmaleic anhydride alternating copolymers have been shown to be useful for imaging of semiconductors at 193 nm (see F. M. Houlihan et al, Macromolecules, 30, pages 6517-6534 (1997); T. Wallow et al., SPIE, Vol. 2724, pages 355-364; and F. M. Houlihan et al., Journal of Photopolymer Science and Technology, 10, No. 3, pages 511-520 (1997)). Several publications are focused on 193 nm resists (i.e., U. Okoroanyanwu et al, SPIE, Vol. 3049, pages 92-103; R. Allen et al., SPIE, Vol. 2724, pages 334-343; and Semiconductor International, September 1997, pages 74-80). Compositions comprising addition polymers and/or ROMP (ring-opening methathesis polymerization) of functionalized norbornenes have been disclosed (e.g., PCT WO 97/33198 (Sep. 12, 1997) to B. F. Goodrich). Homopolymers and maleic anhydride copolymers of norbornadiene and their use in 193 nm lithography have been disclosed (J. Niu and J. Frechet, Angew. Chem. Int. Ed., 37, No. 5, (1998), pages 667-670). No resist compositions for imaging at 157 nm have been disclosed.
Copolymers of fluoroolefin monomers and cyclic unsaturated monomers have been described in U.S. Pat. Nos. 5,177,166 and 5,229,473. These patents do not disclose the use of these copolymers in any photosensitive compositions. Copolymers of certain fluorinated olefins with certain vinyl esters and vinyl ethers have been described. For example, the copolymer of TFE with cyclohexanecarboxylate, vinyl ester is described in Japanese Patent Appl. JP 03281664 and the copolymer of TFE and cyclohexyl vinyl ether is described in Japanese Patent Appl. JP 54046286. Copolymers of TFE and vinyl esters, such as vinyl acetate, and use of these copolymers in photosensitive compositions for refractive index imaging (e.g. holography) is described in U.S. Pat. No. 4,963,471. Disclosures relating to copolymers comprising fluorinated olefins and vinyl esters of formula CH2═CHO2CR and vinyl ethers of formulae CH2═CHOCH2R or CH2═CHOR, have R groups with a C:H ratio that is relatively low and which is less than 0.58.
Homopolymers and copolymers of certain monomers that possess properties of being both cyclic and fluorine-containing have been described as well as their application as components in photodefinable fluorine-containing polymer films in Japanese Kokai No Hei 9(1997)-43856. There is no teaching in this reference of homopolymers or copolymers comprised of polycyclic comonomers as photoresist components. Furthermore, there is no teaching that the compositions disclosed could be used in photoresists with imaging effected at far UV wavelengths of less than 180 nm.
U.S. Pat. No. 5,655,627 discloses a process for generating a negative tone resist image by coating a silicon wafer with a copolymer resist solution of pentafluoropropyl methacrylate-t-butyl methacrylate in a solvent, and then exposing at 193 nm and developing with a carbon dioxide critical fluid.
There is a critical need though for other novel resist compositions for use at 193 nm or lower, and particularly at 157 nm, that have not only high transparency at these short wavelengths but also other suitable key properties, including good plasma etch resistance and adhesive properties.